(1) Field of the Invention
The present invention relates to a method and device for detecting an initial excitation phase of a stepping motor, wherein the initial excitation phase in which a rotor of the stepping motor is stable is detected at a stop position where a reverse rotation of a driven member driven by the stepping motor is forcedly stopped by a stopper.
(2) Description of the Related Art
Recently, a stepping motor has been often used for an on-vehicle meter such as a speed meter or tachometer in terms of indicating accuracy and cost.
However, as for a vehicle in which an on-vehicle meter using such a stepping motor is mounted, by an incorrect drive signal generated due to vehicle vibrations or noises, there might be a problem that an actual amount of movement of a pointer (or indicator) moving in accordance with rotation of the stepping motor is different from an amount of movement thereof, which is originally expected.
Therefore, in an on-vehicle meter using such a stepping motor, for example, at a timing when an ignition key switch is turned on, a pointer or a member of a rotation driving mechanism of the pointer is allowed to abut against a stopper when the pointer rotates in a reverse rotation direction of the pointer (i.e. a direction in which an indicated value on a scale is decreased) so as to conduct an initialization processing, by which the pointer is returned to a zero position defined by the stopper.
During the initialization processing, if an excitation phase is changed to maintain the pointer or the member of the rotation driving mechanism of the pointer rotating in the reverse direction continuously after the pointer or the member abuts against the stopper, the excitation phase is situated less than 180 degrees being viewed from a position of the stopper in a positive rotation direction (i.e. normal rotation direction) of the pointer (i.e. direction in which an indicated value on a scale is increased) so that a magnetic force affecting the rotor in the positive rotation direction from the excitation phase exceeds that in the reverse rotation direction, resulting in that the pointer or the member is instantaneously reversed.
Accordingly, the abutting of the pointer or the member against the stopper must be found out before they are reversed due to the subsequent change in the excitation phase.
Therefore, so far, paying attention to a fact that the excitation phase of the stepping motor indirectly indicates a rotation position of the rotor of the stepping motor and the pointer, an initial excitation phase in which the rotor becomes stable when the pointer or the member abuts against the stopper is set known in advance, so that when the excitation phase of the stepping motor reaches the initial excitation phase, before the pointer or the member (of the rotation driving mechanism of the pointer) reverses, the change in the excitation phase to maintain the pointer to rotate in the reverse direction is stopped.
So far, whether or not the excitation phase of the stepping motor reaches the initial excitation phase has been detected on the basis of a change in an output pattern of two magnetoelectric elements (such as Hall elements) spaced from each other having the same distance as a distance between two magnetic poles adjacent to each other of the rotor (for example, Japanese Patent Application Laid-Open No. H8-322293). Alternatively, it has been detected on the basis of whether or not an induced electromotive force indicating the rotation of the rotor is generated in an exciting coil in a non-excitation state of a stepping motor of full step drive or half step drive (for example, Japanese Patent Application Laid-Open No. 2001-298993).
However, the method using the magnetoelectric elements results in cost-up or a problem that the mechanism becomes complicated due to limitation of the placing position in the proximity of the rotor or deterioration in reliability in a case of avoiding such a limitation. The detection by using the exciting coil in a non-excitation state has a problem that the initial excitation phase can be specified only with a pitch angle of one phase excitation due to a limited detection timing obtained only upon full step driving, therefore the method is not sufficient as a method of detecting the initial excitation phase of the stepping motor of a micro-step drive.